I've got some specific needs, and it would cost me too much to buy the equipment necessary to meet those needs.
So gym it is.
I'm lucky -- turns out there was a Planet Fitness 1.3 miles from my house... right in the same parking lot as the nearest grocery store. (It is seriously tucked off in a corner, where I never really saw it.)
We moved cross-country in 2012. Until then I'd been going regularly. I was lucky -- my physical therapist for his knee had his office INSIDE my gym, so -- since I was a gym member, and at my request -- we could go out on the floor (or to the pool) and he could drill me on what I needed to do.
And I never make New Year's resolutions. Those are just asking for failure.
It's funny... trainers in the gym hear I have a bad knee, and want me on the elliptical. My physical therapist (when I had one)? "I hate those things -- they destroy your knees. Stay off them." (I hadn't needed him to tell me that. Those things hurt!)
If you have bad knees, recumbent bike is your best friend. (I used to do rowing-machine, too, but bike is safer.)
I hate cardio. I used to do cross-country running in high school, and I'm here to tell you I hate cardio.
Weights, on the other hand, make me feel good, and directly affect my every-day life.
I NEED weights, because I have a bad knee. (A big part of my PT for my knee involved increasing the strength of the muscles around the knee, especially abductor/adductor.) Plus, increasing my muscle-mass will decrease my ratio of fat-to-lean, and so decrease my cardiac risk. All good things.
Cardio? Cardio just makes me feel drained.